1. Field Of The Invention
This invention generally relates to electrical terminals for mounting electrical components on printed circuit (PC) boards and, in particular, to a solid single leg terminal suitable for mounting through a mounting hole on a PC board without cutting, deforming or otherwise damaging or affecting the integrity of the PC board.
2. Description Of The Prior Art
The conventional way to mount small electrical terminals (like pins and single leg tabs) on a printed circuit (PC) board is to force the mounting leg of the terminal into a hole on the PC board. The hole diameter is generally smaller than the diagonal or diameter of the mounting leg, so that there is an interference or press fit as shown in FIG. 1. FIG. 2 is an enlarged cross-section of the mounted pin of FIG. 1, showing the interference fit after soldering.
Where a press fit created between the terminal leg and the PC board hole is tight, it produces stresses in the PC board which, if excessive, can crack or warp the board. Also, the insertion force is significantly higher, which may cut into or deform the terminal. An interference fit will also produce board material shavings and excessive board material displacement around the hole which make soldering difficult and can produce a weak solder joint.
In U.S. Pat. No. 4,363,529, the mounting legs establish an interference fit of the legs in the circuit board hole, the legs penetrating the material of the circuit board relatively deeply. It is stresses of this type that the subject invention seeks to eliminate.
An electrical terminal is subject to several different forces (insertion, withdrawal, contact, normal force, vibration, shock, etc.). As above suggested, if the terminal is soldered into the PC board hole with very little interference fit, those forces will be transmitted directly to the solder joint instead of to the board material, which may result in cracking of the solder joint. In an effort to avoid the aforementioned problems, efforts have been made to insure that just the right interference fit exists between the PC board hole and the terminal leg. However, this has necessitated the use of tight tolerances, typically in the range of .+-.0.002 inches.
A number of compliant spade type terminals have been proposed which typically include a pair of spaced legs facing each other, with each of the legs being provided with an outwardly expanded hook portion which forms an elastic contact for compressed fitting with a through hole. The resulting prongs extend through the hole or bore in the printed circuit board to secure the terminal by snapping into place once the prongs have been fully inserted through and exit the hole. Typical of constructions of this type is the terminal disclosed in U.S Pat. No. 4,353,609.
It has also been proposed that the electrically conductive portions of a component or terminal to be mounted be passed through the hole on one side of the circuit board and at least two spaced conductors bent in opposite directions into contact with the soldering conductors or pads on the other side of the board. Typical art of this type is shown in U.S. Pat. No. 3,068,554 and 3,184,532. In the first mentioned patent, a process is disclosed for making magnetic core memory, wherein the ends of staples are bent back against the lower face of the circuit board by the use of a conical mating tool driven between adjacent but spaced staples. In the latter patent, a flaring tool in the shape of a truncated cone is used to bend lead wires of an electrical component toward terminal portions on the bottom of the panel. See also U.S. Pat. Nos. 3,479,634 and 3,536,869. In U.S. Pat. No. 2,869,107, the protruding tabs are twisted to lock the position of the terminal and prevent the tabs from being removed through the openings through which they were inserted.
In some instances, the art has suggested the use of generally cylindrical one legged terminals which are, however, hollow. In U.S. Pat. No. 3,980,367, a hollow-type rivet is deformed by striking it with a hammer or other instrument after it is passed through the hole in the board. Similar terminals are disclosed in U.S. Pat. Nos. 2,990,533; 2,947,964 and 3,445,929, wherein the hollow mounting legs are splayed by various tools.
A circuit board pin is disclosed in U.S. Pat. No. 4,740,166 has a compliant portion formed by two side-by-side beams joined along one edge to produce a longitudinal V-shaped groove. The resulting elastic hinge insures good contact with a conductive sleeve material which lines the through hole.
A terminal tab intended for mounting on a circuit board is disclosed in U.S. Pat. No. 4,436,358 which includes a mounting leg made of flat strip material provided with a longitudinal slot to divide the leg into two sections which are of decreasing width with increasing distance from the base portion mounted on the PC board. The terminal is mounted on a PC board by inserting the tapered leg sections through a hole in the board, the leg portions being deformed or bent in opposite directions by a ram-like member provided on the underneath side of the board. The patentee teaches, however, that the dimensions of the leg should be selected such that a tapered portion of the leg at the upper surface of the board likewise be forced into the circuit board in order to provide an interference fit of the leg in the circuit board.
Thus, the known prior art terminals generally tend to fall into one of two general categories. The first includes mounting legs having at least one dimension greater than the size of the hole through which the mounting leg is placed to cut into the board or otherwise move or deform the board material. The second involves mounting legs which have generally circular cross-sections which can be received within the mounting holes without an interference fit. However, such hollow mounting legs complicate the terminals and increase the manufacturing costs since such terminals cannot simply be made as inexpensively as from strip material nor as easily produced on continuous carrier strips.